The conventional method for facilitating communication between a wireless terminal and a destination computer over a wireless network involves using Transmission Control Protocol (TCP) (RFC 793, Defense Advanced Research Projects Agency) and Internet Protocol (IP) (RFC 791, Defense Advanced Research Projects Agency) over IEEE standard 802.11 protocol. According to this method, the remote land-based computer network associated with the destination computer has a wireless access point server (AP) to allow the destination computer to receive and transmit message data over the wireless network. The wireless terminal would typically run one or more application processes, a TCP layer, an IP layer and a 802.11 layer. The destination computer typically would run one or more application processes, a TCP layer, an IP layer and a IEEE 802.3 layer. The AP typically would run an IEEE 802.3 layer and a 802.11 layer to bridge communications between the wireless terminal and the destination computer.
The application process on the wireless terminal seeking to communicate with a destination process on the destination computer passes message data (eg. via HTTP) to the 802.11 layer via the TCP and IP layers. The 802.11 layer on the wireless terminal then transmits the message data to the 802.11 layer on the AP over the wireless network. Upon receipt of the message data, the 802.11 layer on the AP passes the message data to the 802.3 layer on the AP for retransmission over the land-based computer network. The 802.3 layer on the destination computer passes the message data to the TCP layer (via the IP layer) on the destination computer to verify that the message data was properly received.
If the message data was properly received, the TCP layer on the destination computer passes the data to the application layer, and generates an Acknowledgement (ACK) segment for transmission over the land-based network to the AP. Upon receipt of the ACK, the AP transmits the segment to the wireless terminal over the wireless network. If the TCP layer on the wireless terminal does not receive the ACK segment within a predetermined timeout interval, the TCP layer on the wireless terminal retransmits the message data again.
Although IEEE 802.11 in conjunction with TCP/IP has proven to be useful for facilitating communication between a wireless terminal and a destination computer, both the TCP and the IP layers were designed to facilitate data transmission only over land-based hardwired computer networks. Consequently, if the TCP layer on the wireless terminal does not receive an ACK segment within the predetermined timeout interval the TCP layer assumes that the transmission problem is due to network congestion and increases the interval between segment retransmissions until the ACK segment is finally received. Although this solution may be prudent for data transmission only over land-based hardwired computer networks, this solution can degrade communication performance over wireless networks since the lack of receipt of an ACK segment in a wireless network may be due to the wireless terminal simply drifting out of range of the AP.
Other attempts have been made to provide wireless communication solutions. For instance, one solution, referred to as “Mobile IP”, uses a “home agent server” in communication with the “home” AP associated with the “home” IP sub-net of a wireless terminal, and a “foreign agent server” in communication with the “foreign” AP associated with a “foreign” IP sub-net. When the wireless terminal is located within the home IP sub-net communications area, the home agent server forwards to a destination computer communications datagrams transmitted by the wireless terminal. However, when the wireless terminal roams to the foreign IP sub-net communications, the foreign agent server recognizes that the IP address of the communications datagrams transmitted by the wireless terminal are associated with the home IP sub-net, and forwards the received datagrams to the home agent server for transmission to the destination computer. Although this solution allows a wireless terminal to roam between IP subnets, this solution can degrade communication performance due to the communications processing overhead required to recognize and forward datagrams from a foreign agent server to the home agent server. Further, this solution does not address the TCP retransmission problem, discussed above.
Another solution, referred to as “UDP-Plus”, replaces the TCP layer with a User Datagram Protocol (UDP) layer, and includes a retransmission protocol layer between the application process and the UDP layer. With this solution, if a UDP datagram is not received by the destination process, the retransmission protocol layer of the wireless terminal causes the UDP datagram to be retransmitted until receipt of the UDP datagram is confirmed. However, this solution is deficient in that it increases the resource requirements for the wireless terminal, and does not address the reason for the failed transmission.
Therefore, there remains a need for a data communication system which is optimized for communication over wireless networks.